The present invention generally relates to fuel fired heating appliances, and more particularly relates to air intake and combustion products venting apparatus for high efficiency, fuel fired, induced draft condensing furnaces utilizing direct vents.
Direct vented fuel-fired heating appliances, such as furnaces serving indoor conditioned spaces, have sealed combustion chambers that require appliance intake air and flue gases to be passed through venting systems extended to an outdoor location and terminating within the same outdoor pressure zone.
The combustion systems of modern high efficiency, fuel fired, induced draft condensing furnaces typically include a heat exchanger structure formed from series-connected primary and secondary heat exchanger sections. A fuel/air burner structure is operatively connected to the inlet of the primary heat exchanger, and the inlet of draft inducer fan is coupled to the outlet of the secondary or "condensing" heat exchanger. During operation of the furnace, a fuel/air mixture is delivered to the burner structure which burns the mixture and flows the resulting flames and hot combustion gases into the inlet of the primary or "upstream" heat exchanger section.
At the same time, the draft inducer fan draws the hot combustion gases sequentially through the primary and secondary heat exchanger sections, and then discharges the combustion gases. During this combustion products flow process, supply air to be heated and delivered to a conditioned space served by the furnace is forced externally across the heat exchanger structure to receive combustion heat therefrom.
To supply combustion air to the furnace, and vent combustion gases discharged therefrom to the exterior of the building served by the furnace, it is conventional to respectively extend inlet and vent pipes from the burner structure inlet and the draft inducer fan outlet horizontally outwardly through an exterior wall of the building, or vertically through the roof of the building. Accordingly, during furnace operation the draft inducer fan simultaneously draws outside combustion air through the inlet pipe to the burner structure, and discharges cooled, moisture laden combustion gases (at approximately 120.degree. F.) through the vent pipe to the exterior of the building. Due to the corrosive nature of the cooled combustion gases discharged from a high efficiency condensing furnace of this general type, a preferred material for constructing the overall inlet and vent piping system therefor has been PVC (polyvinyl chloride) plastic pipe.
In horizontal venting and inlet applications, it has been conventional practice to extend the plastic inlet and vent pipes outwardly through the exterior building wall in a relatively close side-by-side relationship, with a vent termination cap structure secured to the exterior ends of the pipes. The cap structure functions to create an axial discharge of the combustion gases and a radial intake of the combustion air to thereby inhibit undesirable short circuiting of the closely adjacent intake and discharge flows at the outer ends of the pipes. In an alternative prior art arrangement the two side-by-side pipes are more widely spaced apart, with the exterior vent pipe portion projecting further away from the exterior building wall than the inlet pipe, and the cap structure is eliminated.
Each of these conventional intake and vent pipe arrangements is subject to several well known and heretofore unsolved problems. One such problem is the tendency of the outer end of the inlet pipe to ice up, and become blocked, during freezing weather due to its proximity to the considerable moisture being discharged with the cooled combustion gases through the adjacent vent pipe. Another problem flows from the tendency of varying outdoor wind velocities and directions to cause undesirable fluctuations in the internal pressure differential across the heat exchanger which, in turn, can adversely affect the venting capabilities of the furnace. This pressure differential fluctuation arises in instances where, due to the outer end geometry of the vent and inlet pipe structure, the outdoor wind pressure at the outer end of the vent pipe is greater or larger than the wind pressure on the outer end of the inlet pipe.
In an attempt to improve the performance of the overall venting and intake system, it has previously been proposed to extend the vent pipe concentrically through a larger diameter inlet pipe passing through the exterior building wall, and to provide the outer end of the larger diameter inlet with a rain shield structure. During operation of this concentric vent termination structure, the cooled combustion gases are axially discharged from the vent pipe, and the incoming combustion air enters the termination assembly in a radial direction through the rain shield structure.
While this prior art concentric vent termination structure tends to alleviate the problem of inlet opening freeze-up, it still tends to create undesirable pressure differential deviations between the inlet and outlet sides of the furnace heat exchanger in response to variations in the outdoor wind velocity and/or direction.
From the foregoing it can be seen that a need exists for an improved horizontal vent termination assembly, for use in conjunction with high efficiency condensing furnaces of the general type described above, which eliminates or at least substantially reduces the above-mentioned problems typically associated with conventionally constructed and configured vent termination assemblies. It is accordingly an object of the present invention to provide such an assembly.